WO2024098966A1

WO2024098966A1 - Heat pump system and control method for heat pump system

Info

Publication number: WO2024098966A1
Application number: PCT/CN2023/119728
Authority: WO
Inventors: 叶文腾; 钟瑞兴; 陈玉辉; 董迎波
Original assignee: 珠海格力电器股份有限公司
Priority date: 2022-11-07
Filing date: 2023-09-19
Publication date: 2024-05-16
Also published as: CN115560493A

Abstract

A heat pump system and a control method for the heat pump system. A refrigerant circulation loop of the heat pump system comprises a main refrigerant pipe (13), an evaporator (3), a compression device, a condenser (4) and a throttling device, the heat pump system having a cooling mode and a heating mode. The compression device comprises a low-pressure-stage compressor (1) and a high-pressure-stage compressor (2). The refrigerant circulation loop further comprises a switching device, and the switching device is configured to enable the refrigerant circulation loop to have a single-compressor working state, in which the high-pressure-stage compressor (2) compresses a refrigerant alone in the cooling mode, and a double-compressor working state, in which the low-pressure-stage compressor (1) and the high-pressure-stage compressor (2) compress the refrigerant in series in the heating mode. In the single-compressor working state, the pressure ratio of the high-pressure-stage compressor (2) is configured to meet the pressure ratio required by the compression device of the heat pump system in the cooling mode; in the double-compressor working state, the pressure ratio of the low-pressure-stage compressor (1) is configured to meet, jointly with that of the high-pressure-stage compressor (2), the pressure ratio required by the compression device of the heat pump system in the heating mode.

Description

Heat pump system and control method of heat pump system

CROSS-REFERENCE TO RELATED APPLICATIONS

This disclosure is based on and claims priority to a Chinese patent application with application number 202211384425.8, application date November 7, 2022, and invention name “Heat pump system and control method for heat pump system”. The disclosure of this Chinese patent application is hereby introduced as a whole into this disclosure.

Technical Field

The present disclosure relates to the technical field of heat pumps, and in particular to a heat pump system and a control method of the heat pump system.

Background technique

Heat pump technology utilizes electricity and suitable low-grade heat sources, and uses a heat pump system to provide thermal energy to meet heat needs such as building heating and domestic hot water. It is the best way to efficiently convert electricity into heat.

The heat pump system has the advantages of environmental protection, energy saving and high efficiency. In recent years, it has been more and more widely used in large-scale central heating systems. In winter, when the heat source temperature is as low as -15°C, the heat pump system produces 50°C hot water, and the required compressor operating pressure ratio is as high as 9.0. The existing heat pump system mainly uses a two-stage centrifugal compressor as a compression device. The maximum pressure ratio of the two-stage centrifugal compressor is about 4.5, and the operating pressure ratio required by the heat pump system when operating in heating mode is far beyond the pressure ratio limit of the two-stage centrifugal compressor. In summer, when the heat pump system is operating in cooling mode, the compression device operating pressure ratio is 3.0. As a result, it is difficult for the two-stage centrifugal compressor to match the high pressure ratio of the heat pump system when it is operating in heating mode and the low pressure ratio when it is operating in cooling mode.

Summary of the invention

The present disclosure aims to provide a heat pump system and a control method for the heat pump system, aiming to solve the problem in the related art that a two-stage centrifugal compressor is difficult to match a high pressure ratio when operating in a heating mode and a low pressure ratio when operating in a cooling mode.

A first aspect of the present disclosure provides a heat pump system, comprising a refrigerant circulation circuit, the refrigerant circulation circuit comprising a main refrigerant pipeline and an evaporator, a compression device, a condenser and a throttling device connected in sequence through the main refrigerant pipeline, the heat pump system having a cooling mode and a heating mode;

The compression device comprises a low-pressure compressor and a high-pressure compressor connected in series through a main refrigerant pipeline, the inlet of the low-pressure compressor is connected to the evaporator through the main refrigerant pipeline, and the outlet of the low-pressure compressor is connected to the evaporator through the main refrigerant pipeline. The refrigerant pipeline is connected to the inlet of the high-pressure compressor, and the outlet of the high-pressure compressor is connected to the condenser through the main refrigerant pipeline;

The refrigerant circulation loop further includes a switching device, which is connected to the main refrigerant pipeline and is configured to enable the refrigerant circulation loop to have a single compressor working state in the cooling mode and a dual compressor working state in the heating mode. In the single compressor working state, the high-pressure stage compressor compresses the refrigerant in the refrigerant circulation loop, and the low-pressure stage compressor stops compressing the refrigerant. In the dual compressor working state, the low-pressure stage compressor and the high-pressure stage compressor are connected in series and compress the refrigerant.

The pressure ratio of the high-pressure stage compressor is configured to satisfy the pressure ratio required by the compression device of the heat pump system in the cooling mode when the single compressor is in operation;

The pressure ratio of the low-pressure stage compressor is configured to satisfy the pressure ratio required by the compression device of the heat pump system in the heating mode together with the high-pressure stage compressor when the two compressors are in operation.

In some embodiments of the heat pump system,

The pressure ratio of the high-pressure stage compressor is configured to be 1.02 to 1.06 times the pressure ratio required by the compression device of the heat pump system in the cooling mode; and/or

The pressure ratio of the low-pressure stage compressor is configured to be 1.04 to 1.06 times the pressure ratio that the low-pressure stage compressor needs to bear when the two compressors are in working state and together with the high-pressure stage compressor meet the pressure ratio required by the compression device of the heat pump system in the heating mode.

In the heat pump system of some embodiments, the switching device includes:

a bypass portion, comprising a bypass pipeline connected to the main refrigerant pipeline in parallel with the low-pressure stage compressor; and

The switching unit is configured to selectively connect one of the bypass line and the low-pressure stage compressor to the refrigerant circulation circuit and disconnect the other from the refrigerant circulation circuit.

In the heat pump system of some embodiments, the switching unit includes a first switching valve, which is disposed on the bypass pipeline and is configured to control the on-off of the bypass pipeline.

In the heat pump system of some embodiments, the refrigerant circulation loop further includes:

a flasher connected to the main refrigerant pipeline between the condenser and the evaporator; and

The gas supply pipeline connects the gas outlet of the flasher and the compression device, and is configured to supply gas to the compression device.

In the heat pump system of some embodiments, the air supply pipeline includes:

a first air supply branch connected between the gas outlet of the flash generator and the inlet of the high-pressure compressor; and/or

The second air supply branch is connected between the gas outlet of the flash generator and the air supply port of the high-pressure compressor.

A series air supply control valve, disposed on the first air supply branch, configured to control the on-off of the first air supply branch; and

The high-pressure air supply control valve is arranged on the second air supply branch and is configured to control the on-off of the second air supply branch.

In the heat pump system of some embodiments, the throttling device includes a first throttling part and a second throttling part connected through the main refrigerant pipeline, and the flasher is located on the main refrigerant pipeline between the first throttling part and the second throttling part.

In the heat pump system of some embodiments, the flash generator is installed on the condenser.

In some embodiments of the heat pump system,

The low-pressure stage compressor is a two-stage centrifugal compressor; and/or

The high-pressure stage compressor is a two-stage centrifugal compressor.

In some embodiments of the heat pump system,

The low-pressure compressor is mounted on the evaporator; and/or

The high-pressure stage compressor is mounted on the condenser.

In some embodiments of the heat pump system,

The low-pressure stage compressor is a fixed-speed compressor; and/or

The high-pressure stage compressor is a fixed-speed compressor.

In some embodiments of the heat pump system,

The low pressure stage compressor includes adjustable inlet guide vanes; and/or

The high pressure stage compressor includes adjustable inlet guide vanes.

In the heat pump system of some embodiments, the flow paths of the low-pressure stage compressor and the high-pressure stage compressor are configured so that F2 = A*F1; wherein

F1 is the volume flow of the low-pressure stage compressor;

F2 is the volume flow of the high pressure compressor;

A is a constant representing the ratio of the outlet specific volume of the high-pressure stage compressor in the cooling mode to the outlet specific volume in the heating mode.

In some embodiments, the heat pump system further includes a water circulation loop, wherein the water circulation loop includes a main water path, A heat source tower and a terminal heat exchanger, wherein the heat source tower is switchably connected to one of the evaporator and the condenser through the main water circuit, and the terminal heat exchanger is switchably connected to the other of the evaporator and the condenser through the main water circuit.

A second aspect of the present disclosure provides a control method for the heat pump system according to the first aspect of the present disclosure, comprising:

In the cooling mode of the heat pump system, the refrigerant circulation loop is placed in the single compressor working state;

In the heating mode of the heat pump system, the refrigerant circulation loop is put into the working state of the two compressors.

In the control method of some embodiments,

The refrigerant circulation loop further includes a flasher and an air supply pipeline, wherein the flasher is connected to the main refrigerant pipeline between the condenser and the evaporator, and the air supply pipeline connects the gas outlet of the flasher and the compression device and is configured to supply air to the compression device;

The control method includes supplying air from the flasher to the compression device through the air supply pipeline.

In the control method of some embodiments, supplying air from the flasher to the compression device comprises:

In the cooling mode of the heat pump system, supplying air to the air supply port of the high-pressure compressor; and/or

In the heating mode of the heat pump system, air is supplied to the air inlet and/or air supply port of the high-pressure stage compressor.

In the control method of some embodiments, the high-pressure stage compressor includes an adjustable inlet guide vane, and the control method also includes adjusting the opening of the adjustable inlet guide vane of the high-pressure stage compressor to change the supplementary air pressure when supplementing air to the compression device.

In the control method of some embodiments,

The low-pressure stage compressor includes an adjustable inlet guide vane; and/or the high-pressure stage compressor includes an adjustable inlet guide vane;

The control method includes: in the heating mode, adjusting the opening of the adjustable inlet guide vane of the low-pressure stage compressor and/or adjusting the opening of the adjustable inlet guide vane of the high-pressure stage compressor so that the low-pressure stage compressor and the high-pressure stage compressor jointly meet the required pressure ratio of the compression device of the heat pump system in the heating mode.

In some embodiments of the control method, the control method includes: in the heating mode, fully opening the adjustable inlet guide vanes of the low-pressure stage compressor, and adjusting the opening degree of the adjustable inlet guide vanes of the high-pressure stage compressor so that the low-pressure stage compressor and the high-pressure stage compressor can jointly meet the required pressure ratio of the compression device of the heat pump system in the heating mode.

Based on the heat pump system provided by the present disclosure, when operating in winter heating mode, the refrigerant circulation loop can be cut off. Switch to the dual compressor working state, use the low-pressure compressor and the high-pressure compressor in series to compress the refrigerant to meet the high pressure ratio requirements for winter heating. At the same time, take into account the cooling needs in summer. When operating in cooling mode, use the high-pressure compressor designed according to the pressure ratio required by the cooling mode to independently compress the refrigerant to match the operating pressure ratio required for refrigeration, which is conducive to ensuring the high efficiency of the high-pressure compressor in single operation in cooling mode. By switching control between single compressor operation and dual compressor series operation, the required operating pressure ratio matching in different operating modes is achieved, which is conducive to ensuring the stability of high-pressure ratio operation in winter heating, and improving the energy efficiency of low-pressure ratio operation in summer cooling.

The control method of the heat pump system according to the embodiment of the present disclosure has the advantages of the heat pump system according to the embodiment of the present disclosure.

Other features and advantages of the present disclosure will become apparent from the following detailed description of exemplary embodiments of the present disclosure with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described herein are used to provide a further understanding of the present disclosure and constitute a part of the present application. The illustrative embodiments of the present disclosure and their descriptions are used to explain the present disclosure and do not constitute an improper limitation on the present disclosure. In the drawings:

FIG1 is a schematic diagram of a heat pump system according to an embodiment of the present disclosure, which shows a refrigerant circulation loop and a water circulation loop of the heat pump system.

FIG. 2 is a schematic diagram of a refrigerant circulation circuit of the heat pump system of the embodiment shown in FIG. 1 .

FIG. 3 is a schematic diagram of the operating characteristics of the compression device of the heat pump system of the embodiment shown in FIG. 1 .

Detailed ways

The technical solutions in the embodiments of the present disclosure will be clearly and completely described below in conjunction with the drawings in the embodiments of the present disclosure. Obviously, the described embodiments are only part of the embodiments of the present disclosure, rather than all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present disclosure and its application or use. Based on the embodiments in the present disclosure, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present disclosure.

Unless otherwise specifically stated, the relative arrangement of the components and steps, numerical expressions, and numerical values described in these embodiments do not limit the scope of the present disclosure. At the same time, it should be understood that for ease of description, the sizes of the various parts shown in the drawings are not drawn according to the actual proportional relationship. The techniques, methods, and devices known to ordinary technicians in the relevant fields may not be discussed in detail, but where appropriate, the techniques, methods, and devices should be considered as part of the authorized specification. In all examples shown and discussed herein, any specific values should be interpreted The present invention is intended to be merely exemplary and not limiting. Therefore, other examples of the exemplary embodiments may have different values. It should be noted that similar reference numerals and letters represent similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further discussed in subsequent drawings.

In the description of the present disclosure, it should be understood that the use of terms such as "first" and "second" to limit components is only for the convenience of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore cannot be understood as limiting the scope of protection of the present disclosure.

In the description of the present disclosure, it should be understood that the orientation or positional relationship indicated by the directional words is usually based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present disclosure and simplifying the description. Unless otherwise specified, these directional words do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the scope of protection of the present disclosure; the directional words "inside and outside" refer to the inside and outside relative to the outline of each component itself.

Fig. 1 is a schematic diagram of a heat pump system according to an embodiment of the present disclosure, which shows a refrigerant circulation loop and a water circulation loop of the heat pump system. Fig. 2 is a schematic diagram of a refrigerant circulation loop of the heat pump system according to the embodiment shown in Fig. 1 .

As shown in FIG. 1 and FIG. 2, an embodiment of the present disclosure provides a heat pump system, including a refrigerant circulation loop, the refrigerant circulation loop including a main refrigerant pipeline 13 and an evaporator 3, a compression device, a condenser 4 and a throttling device connected in sequence through the main refrigerant pipeline 13. The heat pump system has a cooling mode and a heating mode. The compression device includes a low-pressure compressor 1 and a high-pressure compressor 2 connected in series through the main refrigerant pipeline 13, the inlet of the low-pressure compressor 1 is connected to the evaporator 3 through the main refrigerant pipeline 13, the outlet of the low-pressure compressor 1 is connected to the inlet of the high-pressure compressor 2 through the main refrigerant pipeline 13, and the outlet of the high-pressure compressor 2 is connected to the condenser 4 through the main refrigerant pipeline 13. The refrigerant circulation loop also includes a switching device, which is connected to the main refrigerant pipeline 13 and is configured to enable the refrigerant circulation loop to have a single compressor working state in the cooling mode and a double compressor working state in the heating mode. In the single compressor working state, the high-pressure stage compressor 2 independently compresses the refrigerant in the refrigerant circulation loop, and the low-pressure stage compressor 1 stops compressing the refrigerant. In the dual compressor working state, the low-pressure stage compressor 1 and the high-pressure stage compressor 2 are connected in series and compress the refrigerant.

The pressure ratio of the high-pressure stage compressor 2 is configured to meet the pressure ratio required by the compression device of the heat pump system in the cooling mode when operating in a single compressor working state.

The pressure ratio of the low-pressure stage compressor 1 is configured to meet the pressure ratio required by the compression device of the heat pump system in the heating mode together with the high-pressure stage compressor 2 when operating in the dual compressor working state.

According to the heat pump system of the embodiment of the present disclosure, when the heat pump system is operated in the heating mode in winter, the refrigerant circulation loop can be switched to the double compressor working state, using the low-pressure compressor 1 and the high-pressure compressor 2. The compressors are connected in series to compress the refrigerant to meet the high pressure ratio requirements for winter heating. For example, hot water at 50°C can be produced normally when the heat source temperature is -15°C. At the same time, taking into account the cooling needs in summer, when the heat pump system is running in cooling mode, only the high-pressure compressor 2 is turned on. The high-pressure compressor 2 designed according to the pressure ratio required by the cooling mode is used to independently compress the refrigerant to match the operating pressure ratio required for refrigeration, which is conducive to ensuring the high efficiency of the high-pressure compressor in single operation in cooling mode. By switching control between single compressor operation and double compressor series operation, the required operating pressure ratio matching in different operating modes is achieved, which is conducive to ensuring the stability of high-pressure ratio operation in winter heating and improving the energy efficiency of low-pressure ratio operation in summer cooling.

In some embodiments of the heat pump system, the pressure ratio of the high-pressure stage compressor 2 is configured to be 1.02 to 1.05 times the pressure ratio required by the compression device of the heat pump system in the cooling mode; and/or the pressure ratio of the low-pressure stage compressor 1 is configured to be 1.04 to 1.06 times the pressure ratio that the low-pressure stage compressor 1 needs to bear when the two compressors are in the working state and together with the high-pressure stage compressor 2 meet the pressure ratio required by the compression device of the heat pump system in the heating mode.

The above arrangement allows unpredictable factors in the actual operation of the heat pump system to be taken into consideration when designing the corresponding pressure ratios of the low-pressure stage compressor 1 and the high-pressure stage compressor 2, and a certain margin is reserved when designing the pressure ratio.

FIG3 is a schematic diagram of the operating characteristics of the low-pressure compressor and the high-pressure compressor of the heat pump system of the embodiment shown in FIG1. In FIG3, the horizontal axis F represents the volume flow rate, the vertical axis R represents the pressure ratio, and each curve represents:

L1 is the surge line;

L2 is the pipe network characteristic curve under the working state of two compressors;

L3 is the pipe network characteristic curve under the working state of a single compressor;

C1 is the characteristic curve of the compression device under the working state of two compressors;

C2 is the characteristic curve of low-pressure compressor 1 when the opening of its adjustable inlet guide vane is 100% under the dual compressor working state;

C3 is the characteristic curve of the high-pressure stage compressor 2 when the opening of its adjustable inlet guide vane is 100% under the single compressor working state;

C4 is the characteristic curve of the high-pressure stage compressor 2 when the opening of its adjustable inlet guide vane is less than 100% under the single compressor working state;

F1 is the volume flow of the low-pressure stage compressor 1, hereinafter referred to as the first volume flow;

F2 is the volume flow of the high pressure stage compressor 2, hereinafter referred to as the second volume flow;

R1 is the pressure ratio of the compression device when the exhaust volume of the compression device is the first volume flow F1 under the working state of two compressors, hereinafter referred to as the first pressure ratio;

R2 is the low-pressure compression when the exhaust volume of the compression device is the first volume flow F1 under the working state of the two compressors. The pressure ratio of the machine 1 when the opening of its adjustable inlet guide vane is 100%, hereinafter referred to as the second pressure ratio;

R3 is the pressure ratio of the high-pressure stage compressor 2 when the exhaust volume of the compression device is the first volume flow F1 under the working state of the two compressors and the opening of the adjustable inlet guide vane is less than 100%, hereinafter referred to as the third pressure ratio;

R4 is the pressure ratio of the high-pressure stage compressor 2 when the adjustable inlet guide vane opening is 100% when the exhaust volume of the compression device is the second volume flow F2 in the single compressor working state, hereinafter referred to as the fourth pressure ratio.

The first pressure ratio R1, the second pressure ratio R2 and the third pressure ratio all correspond to the first volume flow F1. The first pressure ratio R1 refers to the total pressure ratio of the compression device for the heating demand of the heat pump system, that is, the pressure ratio of the compression device when the low-compression compressor 1 and the high-pressure compressor 2 work in series to compress the refrigerant under the working state of two compressors, and the two compressors operate at the second pressure ratio R2 and the third pressure ratio R3 respectively. The first pressure ratio R1 = the second pressure ratio R2 * the third pressure ratio R3.

The fourth pressure ratio R4 corresponds to the second volume flow F2. In the single compressor working state, the high pressure stage compressor 2 works alone to compress the refrigerant to meet the refrigeration demand of the heat pump system.

The pressure ratio required by the compression device of the aforementioned heat pump system in the cooling mode is the fourth pressure ratio R4. The pressure ratio of the high-pressure stage compressor 2 is configured to be 1.02 to 1.05 times the pressure ratio required by the compression device of the heat pump system in the cooling mode, that is, the pressure ratio of the high-pressure stage compressor 2 is configured to be 1.02 to 1.05 times, for example, 1.03 times, of the fourth pressure ratio R4.

The pressure ratio that the low-pressure compressor 1 needs to bear when the two compressors work together with the high-pressure compressor 2 to meet the required pressure ratio of the compression device of the heat pump system in the heating mode is the second pressure ratio R2. The pressure ratio of the low-pressure compressor 1 is configured to be 1.01 to 1.08 times the pressure ratio that the low-pressure compressor 1 needs to bear when the two compressors work together with the high-pressure compressor 2 to meet the required pressure ratio of the heat pump system in the heating mode, that is, the pressure ratio of the low-pressure compressor 1 is configured to be 1.01 to 1.08 times, for example, 1.06 times, of the second pressure ratio R2.

As shown in Fig. 1 and Fig. 2, in the heat pump system of some embodiments, the switching device includes a bypass part and a switching part. The bypass part includes a bypass line 14 connected in parallel with the low-pressure stage compressor 1. The switching part is configured to selectively connect one of the bypass line 14 and the low-pressure stage compressor 1 to the refrigerant circulation circuit, and disconnect the other from the refrigerant circulation circuit.

As shown in FIG. 1 and FIG. 2 , in the heat pump system of some embodiments, the switching unit includes a first switching valve 6, which is disposed on the bypass line 14 and is configured to control the on-off of the bypass line 14. When the first switching valve 6 is opened, the refrigerant passes through the bypass line 14, the low-pressure stage compressor 1 does not participate in the compression of the refrigerant, and the high-pressure stage compressor 2 alone compresses the refrigerant. When the first switching valve 6 is disconnected, the low-pressure stage compressor 1 and the high-pressure stage compressor 2 work in series to compress the refrigerant. The first switching valve 6 is, for example, an electric valve, such as an electric butterfly valve.

In an embodiment not shown in the figure, a second switching valve can also be provided. The second switching valve can be provided on the main refrigerant pipeline 13 between the inlet of the low-pressure stage compressor 1 and the bypass pipeline 14 or on the main refrigerant pipeline 13 between the outlet of the low-pressure stage compressor 1 and the bypass pipeline 14.

As shown in Figures 1 and 2, in the heat pump system of some embodiments, the refrigerant circulation loop further includes a flasher 5 and an air supply pipeline. The flasher 5 is connected to the main refrigerant pipeline 13 between the condenser 4 and the evaporator 3. The air supply pipeline connects the gas outlet of the flasher 5 and the compression device, and is configured to supply air to the compression device.

In the embodiment shown in FIG. 1 and FIG. 2 , the air supply pipeline includes at least one of a first air supply branch 15 and a second air supply branch 16. The first air supply branch 15 is connected between the gas outlet of the flasher 5 and the inlet of the high-pressure compressor 2. The second air supply branch 16 is connected between the gas outlet of the flasher 5 and the air supply port of the high-pressure compressor 2.

In the embodiment shown in FIG. 1 and FIG. 2 , the refrigerant circulation loop includes at least one of a series air supply control valve 8 and a high-pressure air supply control valve 9. The series air supply control valve 8 is arranged on the first air supply branch 15 and is configured to control the on-off of the first air supply branch 15. The high-pressure air supply control valve 9 is arranged on the second air supply branch 16 and is configured to control the on-off of the second air supply branch 16.

The series air supply control valve 8 and the high-pressure air supply control valve 9 are, for example, electric valves, which may be electric butterfly valves, electric ball valves, or solenoid valves.

As shown in FIG. 1 and FIG. 2 , the throttling device includes a first throttling portion 11 and a second throttling portion 12 connected by a main refrigerant pipeline 13 , and the flasher 5 is located on the main refrigerant pipeline 13 between the first throttling portion 11 and the second throttling portion 12 .

In the heat pump system of some embodiments, the flash generator 5 is installed on the condenser 4 .

In the heat pump system of some embodiments, the refrigerant circulation loop may further include a check valve, which is disposed on the main refrigerant pipeline 13 between the outlet of the high-pressure compressor 2 and the condenser 4. The check valve helps prevent the high-pressure gas in the condenser 4 from flowing back when the compression device is shut down, causing the compression device to reverse.

As shown in FIG. 1 and FIG. 2 , in the heat pump system of some embodiments, the low-pressure stage compressor 1 and the high-pressure stage compressor 2 may both be centrifugal compressors, for example, the low-pressure stage compressor 1 is a two-stage centrifugal compressor; the high-pressure stage compressor 2 is a two-stage centrifugal compressor.

In some embodiments, to facilitate adjusting the pressure ratio, the low-pressure stage compressor 1 is a fixed-speed compressor; and/or the high-pressure stage compressor 2 is a fixed-speed compressor. For example, the low-pressure stage compressor and the high-pressure stage compressor can both be fixed-frequency centrifugal compressors.

The low-pressure compressor 1 includes an adjustable inlet guide vane; and/or the high-pressure compressor 2 includes an adjustable inlet guide vane. This arrangement is conducive to adjusting the refrigerant flow and pressure of the heat pump system according to different working conditions of the heat pump system.

In the heat pump system of some embodiments, the flow passages of the low-pressure compressor 1 and the high-pressure compressor 2 are configured so that F2 = A*F1. Where F1 is the volume flow of the low-pressure compressor; F2 is the volume flow of the high-pressure compressor. A is a constant representing the ratio of the outlet specific volume of the high-pressure compressor 2 in the cooling mode to the outlet specific volume in the heating mode.

In heating mode, since the two compressors need to run in series, after the refrigerant gas is compressed by the low-pressure compressor 1, the gas specific volume decreases, and the required flow channel is narrow when it reaches the high-pressure compressor 2. The high-pressure compressor 2 is designed based on the refrigeration mode, with a low pressure ratio, a large gas specific volume, and a wide flow channel. Therefore, when designing the high-pressure compressor 2, when selecting the volume flow, it is necessary to design the ratio of the first volume flow F1 of the low-pressure compressor 1 and the second volume flow F2 of the high-pressure compressor 2, that is, the second volume flow F2 = A*the first volume flow F1, to ensure that the flow channel of the high-pressure compressor 2 in the refrigeration mode and the heating mode is within a reasonable range.

The constant A is described below.

The outlet specific volume _V2 of the high-pressure compressor 2 in both the cooling mode and the heating mode is as follows:
_V2 = _Vin /(P2/P1)1/k.

Where Vin is the inlet specific volume of the high-pressure compressor 2, P2 is the outlet pressure of the high-pressure compressor 2, P1 is the inlet pressure of the high-pressure compressor 2, and k is the adiabatic index. The above parameters are different in cooling mode and heating mode, so the outlet specific volume of the high-pressure compressor 2 is different in cooling mode and heating mode. Therefore, a constant A can be used to represent the ratio of the outlet specific volume of the high-pressure compressor 2 in cooling mode to the outlet specific volume in heating mode.

In the heat pump system of some embodiments, the low-pressure stage compressor 1 is installed on the evaporator 3 , and the high-pressure stage compressor 2 is installed on the condenser 4 .

As shown in Figure 1, in the heat pump system of some embodiments, the heat pump system also includes a water circulation loop, the water circulation loop includes a main water line 77, a heat source tower 71 and a terminal heat exchanger 73, the heat source tower 71 is switchably connected to one of the evaporator 3 and the condenser 4 through the main water line 77, and the terminal heat exchanger 73 is switchably connected to the other of the evaporator 3 and the condenser 4 through the main water line 77.

As shown in FIG1 , the heat pump system of the embodiment of the present disclosure includes a refrigerant circulation circuit and a water circulation circuit as shown in FIG2 . The refrigerant circulation circuit refers to the previous description, and the water circulation circuit mainly includes a main water circuit 77, a heat source tower 71, a first circulation water pump 72, a terminal heat exchanger 73, a second circulation water pump 74, a working mode switching unit 70, a concentrating device 75, a third circulation water pump 76, and a concentrating branch 78. The heat source tower 71 and the first circulation water pump 72 are connected in series through the main water circuit 77, and are switchably connected to one of the evaporator 3 and the condenser 4 through the working mode switching unit 70. The terminal heat exchanger 73 and the second circulation water pump 74 are connected in series through the main water circuit 77, and are switchably connected to the other of the evaporator 3 and the condenser 4 through the main water circuit 77 and the working mode switching unit 70.

For example, when the working mode switching unit 70 is switched to the state shown in FIG. 1 , the heat source tower 71, the first circulating water pump 72, the working mode switching unit 70 and the evaporator 3 are sequentially connected through the main water path 77 to form a circulation loop; at the same time, The terminal heat exchanger 73, the second circulating water pump 74, the working mode switching unit 70 and the condenser 4 are connected in sequence through the main water path 77 to form a circulation loop. At this time, the heat pump system is in the heating mode.

In a refrigeration mode not shown in the figure, the working mode switching unit 70 can be switched to connect the heat source tower 71, the first circulating water pump 72, the working mode switching unit 70 and the condenser 4 in sequence through the main water channel 77 to form a circulation loop; at the same time, the terminal heat exchanger 73, the second circulating water pump 74, the working mode switching unit 70 and the evaporator 3 are connected in sequence through the main water channel 77 to form a circulation loop.

The first circulating water pump 72 is used to provide power for the circulating loop where the heat source tower 71 is located, and the second circulating water pump 72 is used to provide power for the circulating loop where the terminal heat exchanger 73 is located.

The concentrating device 75 , the third circulating water pump 76 , and the concentrating branch 78 are configured to concentrate and store the antifreeze liquid.

The operation process of the embodiment of the present disclosure is described below in conjunction with FIG. 1 and FIG. 2 .

In the heating mode, the first switching valve 6 is closed, the series air supply control valve 8 is opened, and the high-pressure air supply control valve 9 is closed. The gaseous refrigerant in the evaporator 3 is compressed by the low-pressure compressor 1 and discharged, enters the high-pressure compressor 2 for further compression, and is discharged into the condenser 4. The liquid refrigerant in the condenser 4 enters the flasher 5 after the first throttling of the first throttling part 11. The gaseous refrigerant after flashing is mixed with the exhaust gas of the low-pressure compressor 1 through the series air supply control valve 8, and then enters the high-pressure compressor 2. The liquid refrigerant after flashing enters the evaporator 3 after the second throttling of the second throttling part 12, thereby realizing the cycle.

In the cooling mode, the first switching valve 6 is opened, the series air supply control valve 8 is closed, and the high-pressure air supply control valve 9 is opened. The gaseous refrigerant of the evaporator 3 directly enters the high-pressure compressor 2 through the first switching valve 6 for compression, and then is discharged into the condenser 4. The liquid refrigerant of the condenser 4 enters the flasher 5 after primary throttling through the first throttling part 11. The gaseous refrigerant after flashing enters the air supply port of the high-pressure compressor 2 through the high-pressure air supply control valve 9. The liquid refrigerant after flashing enters the evaporator 3 after secondary throttling through the second throttling part 12, thereby realizing circulation.

The present disclosure also provides a control method for the heat pump system of the present disclosure. The control method includes: in the cooling mode of the heat pump system, the refrigerant circulation loop is in a single compressor working state; in the heating mode of the heat pump system, the refrigerant circulation loop is in a dual compressor working state.

The control method of the embodiment of the present disclosure has the same advantages as the heat pump system of the embodiment of the present disclosure.

In the control method of some embodiments, the refrigerant circulation loop also includes a flasher 5 and an air supply pipeline. The flasher 5 is connected to the main refrigerant pipeline 13 between the condenser 4 and the evaporator 3. The air supply pipeline connects the gas outlet of the flasher 5 and the compression device, and is configured to supply air to the compression device. The control method includes supplying air from the flasher 5 to the compression device.

In the control method of some embodiments, in the cooling mode of the heat pump system, air is supplied to the air supply port of the high-pressure stage compressor 2; and/or in the heating mode of the heat pump system, air is supplied to the air supply port and/or the air inlet of the high-pressure stage compressor 2.

In the control method of some embodiments, the control method further comprises adjusting the opening of the adjustable inlet guide vane of the high-pressure stage compressor 2 to change the supplementary air pressure when supplementing air to the compression device.

In the control method of some embodiments, the control method includes: in the heating mode, adjusting the opening of the adjustable inlet guide vane of the low-pressure stage compressor 1 and/or adjusting the opening of the adjustable inlet guide vane of the high-pressure stage compressor 2 so that the low-pressure stage compressor 1 and the high-pressure stage compressor 2 can jointly meet the pressure ratio required by the compression device of the heat pump system in the heating mode.

In the control method of some embodiments, the control method includes: in the heating mode, fully opening the adjustable inlet guide vanes of the low-pressure stage compressor 1, and adjusting the opening degree of the adjustable inlet guide vanes of the high-pressure stage compressor 2 so that the low-pressure stage compressor 1 and the high-pressure stage compressor 2 can jointly meet the pressure ratio required by the compression device of the heat pump system in the heating mode.

According to the above description, the heat pump system and the control method of the heat pump system according to the embodiment of the present disclosure have at least one of the following advantages:

When heating in winter, a low-pressure compressor and a high-pressure compressor are connected in series to compress the refrigerant, which is conducive to achieving the high pressure ratio required for winter heating. When cooling in summer, a high-pressure compressor is used to compress the refrigerant alone to match the operating pressure ratio required for cooling. This is conducive to ensuring stability when operating at a high pressure ratio for winter heating, and improving energy efficiency when operating at a low pressure ratio for summer cooling.

When both compressors are two-stage compressors, the two compressors in series compressing the refrigerant is equivalent to a four-stage compressor compressing the refrigerant, which is more conducive to meeting the high pressure ratio required for winter heating.

During summer cooling, a high-pressure compressor can be used to compress the refrigerant alone, which is also conducive to better matching the flow and pressure ratio, avoiding the "small horse pulling a big cart" phenomenon, and also conducive to improving the operating stability of the heat pump system.

The refrigerant circulation loop of the heat pump system is equipped with a flasher. When two compressors are working, air can be supplied from the middle of the two compressors. When a single compressor is working, air can be supplied from the air supply port of the running high-pressure compressor. The pressure ratio is balanced by switching the air supply, thus achieving efficient operation in dual working conditions.

The flash unit is installed on the condenser, the low-pressure compressor is installed on the evaporator, and the high-pressure compressor and the flash unit are installed on the condenser, which is conducive to the compact overall structure of the heat pump system and saves the installation area of the project.

In heating mode, the two compressors are turned on at the same time, and the adjustable inlet guide vanes of the low-pressure compressor are kept fully open. The low-pressure compressor is operated at a high pressure ratio by adjusting the opening of the adjustable inlet guide vanes of the high-pressure compressor, and the high-pressure compressor can match the remaining required pressure ratio of the compression device, ensuring that the first pressure ratio R1 = the second pressure ratio R2 * the third pressure ratio R3, thereby realizing series operation in heating mode and facilitating reliable operation of the two compressors.

The supply air pressure can be regulated by adjusting the opening of the adjustable inlet guide vane of the high-pressure compressor. This is because the exhaust pressure of the low-pressure compressor can be controlled by adjusting the opening of the adjustable inlet guide vane of the high-pressure compressor, thereby affecting the supply air pressure. The opening of the adjustable inlet guide vane of the high-pressure compressor is closed to increase the back pressure of the low-pressure compressor. The supply air needs to overcome this back pressure to send the gas into the high-pressure compressor. On the contrary, the opening of the adjustable inlet guide vane of the high-pressure compressor is increased to reduce the back pressure of the low-pressure compressor, and the supply air pressure is appropriately reduced. Therefore, the supply air pressure can be intervened by adjusting the opening of the adjustable inlet guide vane of the high-pressure compressor.

In cooling mode, the user's cooling mode needs are met by turning on the high-pressure compressor alone. At this time, the adjustable inlet guide vanes of the high-pressure compressor can be used to adjust the flow rate to meet the user's different load requirements.

The two compressors use fixed-speed compressors and utilize fixed-speed compatible pneumatic technology. The high-pressure stage compressor is designed according to the cooling mode, and the low-pressure stage compressor is designed according to the heating mode. The pressure ratio is redistributed by adjusting the opening of the adjustable inlet guide vanes of the high-pressure stage compressor, which is conducive to achieving a large pressure ratio in the heating mode and high-efficiency operation in the cooling mode.

The low-pressure compressor adopts a single-stage theoretical cycle design without air supplementation, and the high-pressure compressor adopts a two-stage theoretical cycle design with air supplementation, which is conducive to air supplementation and enthalpy increase when the working condition is switched to improve the operating efficiency of the cooling mode. When the heat pump system is running in heating mode and cooling mode, the working condition is switched through the air supplement valve, and the pressure of the flasher is controlled by adjusting the adjustable inlet guide vane opening of the high-pressure compressor, which is conducive to the redistribution of the pressure ratio of the low-pressure compressor and the high-pressure compressor.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present disclosure rather than to limit it. Although the present disclosure has been described in detail with reference to the preferred embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present disclosure can still be modified or some technical features can be replaced by equivalents, which should all be included in the scope of the technical solution for protection requested by the present disclosure.

Claims

A heat pump system comprises a refrigerant circulation circuit, wherein the refrigerant circulation circuit comprises a main refrigerant pipeline (13) and an evaporator (3), a compression device, a condenser (4) and a throttling device which are sequentially connected via the main refrigerant pipeline (13), wherein the heat pump system has a cooling mode and a heating mode, wherein:

The compression device comprises a low-pressure compressor (1) and a high-pressure compressor (2) connected in series via a main refrigerant pipeline (13); the inlet of the low-pressure compressor (1) is connected to the evaporator (3) via the main refrigerant pipeline (13); the outlet of the low-pressure compressor (1) is connected to the inlet of the high-pressure compressor (2) via the main refrigerant pipeline (13); and the outlet of the high-pressure compressor (2) is connected to the condenser (4) via the main refrigerant pipeline (13);

The refrigerant circulation loop also includes a switching device, which is connected to the main refrigerant pipeline (13) and is configured to enable the refrigerant circulation loop to have a single compressor working state in the cooling mode and a dual compressor working state in the heating mode. In the single compressor working state, the high-pressure stage compressor (2) compresses the refrigerant in the refrigerant circulation loop, and the low-pressure stage compressor (1) stops compressing the refrigerant. In the dual compressor working state, the low-pressure stage compressor (1) and the high-pressure stage compressor (2) are connected in series and compress the refrigerant.

The pressure ratio of the high-pressure stage compressor (2) is configured to satisfy the pressure ratio required by the compression device of the heat pump system in the refrigeration mode when the single compressor is in operation;

The pressure ratio of the low-pressure stage compressor (1) is configured to satisfy the pressure ratio required by the compression device of the heat pump system in the heating mode together with the high-pressure stage compressor (2) when the two compressors are in operation.
The heat pump system according to claim 1, wherein:

The pressure ratio of the high-pressure compressor (2) is configured to be 1.02 to 1.06 times the pressure ratio required by the compression device of the heat pump system in the cooling mode; and/or

The pressure ratio of the low-pressure stage compressor (1) is configured to be 1.04 to 1.06 times the pressure ratio that the low-pressure stage compressor (1) needs to bear when the two compressors are in the working state and together with the high-pressure stage compressor (2) meet the pressure ratio required by the compression device of the heat pump system in the heating mode.
The heat pump system according to claim 1 or 2, wherein the switching device comprises:

a bypass portion, comprising a bypass pipeline (14) connected to the main refrigerant pipeline (13) in parallel with the low-pressure stage compressor (1); and

The switching unit is configured to selectively connect one of the bypass line (14) and the low-pressure stage compressor (1) to the refrigerant circulation circuit and disconnect the other from the refrigerant circulation circuit.
The heat pump system according to claim 3, wherein the switching unit comprises a first switching valve (6), the first switching valve (6) being arranged on the bypass pipeline (14) and configured to control the on-off of the bypass pipeline (14).
The heat pump system according to any one of claims 1 to 4, wherein the refrigerant circulation circuit further comprises:

a flasher (5) connected to the main refrigerant pipeline (13) between the condenser (4) and the evaporator (3); and

The air supply pipeline connects the gas outlet of the flash device (5) and the compression device, and is configured to supply air to the compression device.
The heat pump system according to claim 5, wherein the air supply pipeline comprises:

A first air supply branch (15) connected between the gas outlet of the flash generator (5) and the inlet of the high-pressure compressor (2); and/or

The second air supply branch (16) is connected between the gas outlet of the flash generator (5) and the air supply port of the high-pressure compressor (2).
The heat pump system according to claim 6, wherein the refrigerant circulation loop further comprises:

A series air supply control valve (8), arranged on the first air supply branch (15), configured to control the on-off of the first air supply branch (15); and

The high-pressure air supply control valve (9) is arranged on the second air supply branch (16) and is configured to control the on-off of the second air supply branch (16).
A heat pump system according to any one of claims 5 to 7, wherein the throttling device comprises a first throttling portion (11) and a second throttling portion (12) connected via the main refrigerant pipeline (13), and the flasher (5) is located on the main refrigerant pipeline (13) between the first throttling portion (11) and the second throttling portion (12).
The heat pump system according to any one of claims 5 to 8, wherein the flash generator (5) is installed on the condenser (4).
A heat pump system according to any one of the preceding claims, wherein:

The low-pressure stage compressor (1) is a two-stage centrifugal compressor; and/or

The high-pressure stage compressor (2) is a two-stage centrifugal compressor.
A heat pump system according to any one of the preceding claims, wherein:

The low-pressure compressor (1) is mounted on the evaporator (3); and/or

The high-pressure compressor (2) is installed on the condenser (4).
A heat pump system according to any one of the preceding claims, wherein:

The low-pressure stage compressor (1) is a fixed-speed compressor; and/or

The high-pressure compressor (2) is a fixed-speed compressor.
A heat pump system according to any one of the preceding claims, wherein:

The low-pressure stage compressor (1) comprises adjustable inlet guide vanes; and/or

The high pressure stage compressor (2) comprises adjustable inlet guide vanes.
The heat pump system according to any one of the preceding claims, wherein the flow passages of the low-pressure stage compressor (1) and the high-pressure stage compressor (2) are configured so that F2 = A*F1;

F1 is the volume flow of the low-pressure stage compressor (1);

F2 is the volume flow of the high pressure compressor (1);

A is a constant representing the ratio of the outlet specific volume of the high-pressure stage compressor (2) in the cooling mode to the outlet specific volume in the heating mode.
The heat pump system according to any one of the preceding claims further comprises a water circulation loop, wherein the water circulation loop comprises a main water path (77), a heat source tower (71) and a terminal heat exchanger (73), wherein the heat source tower (71) is switchably connected to one of the evaporator (3) and the condenser (4) through the main water path (77), and the terminal heat exchanger (73) is switchably connected to the evaporator (3) and the condenser (4) through the main water path (77). (4) Another connection.
A control method for a heat pump system according to any one of the preceding claims, comprising:

In the cooling mode of the heat pump system, the refrigerant circulation loop is placed in the single compressor working state;

In the heating mode of the heat pump system, the refrigerant circulation loop is put into the working state of the two compressors.
The control method according to claim 16, wherein:

The refrigerant circulation loop further comprises a flasher (5) and an air supply pipeline, wherein the flasher (5) is connected to the main refrigerant pipeline (13) between the condenser (4) and the evaporator (3), and the air supply pipeline connects the gas outlet of the flasher (5) and the compression device, and is configured to supply air to the compression device;

The control method comprises supplying air from the flasher (5) to the compression device through the air supply pipeline.
The control method according to claim 17, wherein supplying air from the flasher (5) to the compression device comprises:

In the cooling mode of the heat pump system, supplying air to the air supply port of the high-pressure compressor (2); and/or

In the heating mode of the heat pump system, air is supplied to the air inlet and/or air supply port of the high-pressure compressor (2).
The control method according to claim 17 or 18, wherein the high-pressure stage compressor (2) includes an adjustable inlet guide vane, and the control method further comprises adjusting the opening of the adjustable inlet guide vane of the high-pressure stage compressor (2) to change the air supply pressure when supplying air to the compression device.
The control method according to any one of claims 16 to 19, wherein:

The low-pressure stage compressor (1) comprises an adjustable inlet guide vane; and/or the high-pressure stage compressor (2) comprises an adjustable inlet guide vane;

The control method comprises: in the heating mode, adjusting the opening of the adjustable inlet guide vane of the low-pressure stage compressor (1) and/or adjusting the opening of the adjustable inlet guide vane of the high-pressure stage compressor (2) so that the low-pressure stage compressor (1) and the high-pressure stage compressor (2) jointly meet the requirements of the heat pump system in the heating mode. The required pressure ratio of the compression device.
The control method according to claim 20 comprises: in the heating mode, fully opening the adjustable inlet guide vanes of the low-pressure stage compressor (1), and adjusting the opening degree of the adjustable inlet guide vanes of the high-pressure stage compressor (2) so that the low-pressure stage compressor (1) and the high-pressure stage compressor (2) can jointly meet the required pressure ratio of the compression device of the heat pump system in the heating mode.